1. Field of the Invention
The present invention relates to a process for producing a printed circuit board and the printed circuit board obtained by the process. Particularly, it relates to a process for efficiently producing a printed circuit board excellent in dielectric properties, dimensional stability and flexing properties and the printed circuit board obtained by the process.
2. Description of the Related Arts
Hitherto, composite sheets which are the combinations of thermosetting resins such as an epoxy resin, a phenol resin or an unsaturated polyester resin with materials such as paper, a glass fiber or a synthetic fiber have been widely used as insulating materials for printed circuit boards. These composite base materials are excellent in electrical insulating properties and are in increasing demand in the electric and electronic fields.
The composite base materials comprising a thermosetting resin, however, is molded with use of a solvent such as a styrene monomer and has a bad environment of molding operation, so that they are not suitable for a multi-layer printed circuit board used in the fields such as computer industry where high-speed operation is required.
As the multi-layer printed circuit board used in the fields such as computer industry where high-speed operation is required, printed circuit boards which comprise a fluorinated polyethylene resin as an insulating base material have been recently developed with great strides.
However, fluorinated polyethylene resins are very difficult to mold, so that the development molded articles of usual melt molding, specifically injection molding or extrusion molding has been investigated. Printed circuit boards comprising as a base material polyphenylene sulfide (PPS) which is a thermoplastic resin have also been researched for improving the production efficiency, but they have a problem that they have too high dielectric constant to use them as a multi-layer printed circuit board for the high-speed operation.
Thus, the present inventor has earnestly conducted researches for the development of a process for efficiently producing a printed circuit board which is excellent in dielectric properties, dimensional stability and flexing properties under a good operation environment.
As a result, the present inventors have found that a printed circuit board having the aforementioned properties can be obtained by using a composition of a styrene polymer having a syndiotactic structure (hereinafter referred to as SPS), a fibrous filler, a binder and/or a binding fiber at a predetermined ratio, molding the composition according to the principle of papermaking and finally providing a metal layer on the molded product thus obtained. The present invention has been accomplished on the basis of the finding.